1. Field of the Invention
The present invention relates to precursor compositions that are useful for the fabrication of passive electronic components and features such as resistors, inductors and capacitors. The precursor compositions can have a low conversion temperature to enable low-temperature treatment of the precursors to form electronic features on a variety of substrates. The precursor compositions have a low viscosity and can advantageously be deposited using a direct-write tool and subsequently converted to the passive electronic feature.
2. Description of Related Art
A variety of materials are used to create electronic circuitry on a substrate. Examples include metals and other conductive materials for electrical conductors, dielectric materials for insulation and capacitive elements, resistive materials for resistors, ferroelectric materials for capacitive elements and magnetic materials for inductors.
Dielectric materials have a wide variety of applications in electronic circuits. They are used to provide electrical insulation as well as to facilitate the temporary storage of electrical charge. The dielectric constant, dielectric loss factor, and dielectric strength determine the suitability for a specific application. Variations in dielectric properties with frequency, temperature, and a range of environmental conditions such as humidity also play a role in determining the usefulness of any particular material composition.
Most resistors for integrated electronic applications are required to be ohmic, to display small deviations from their predetermined value (tolerance), and to have small temperature coefficients of resistance (TCR). TCR is an expression of change in resistance due to change in temperature and it is expressed in parts per million per degree Celsius (ppm/° C.). The TCR of conductive and semiconductive materials can be either positive (increasing resistance with increase in temperature) or negative (decreasing resistance with increasing temperature).
The major demand for resistors in electronic applications lies in the resistance range from 103 to 108 Ω. This is a serious challenge, as pure materials with suitable and reliable electrical behavior typically have resistivities below about 10−6 Ω-m. Unfortunately there are no pure, single-phase materials that provide optimum properties for ohmic resistors. The key to producing a resistor with a specific resistivity and low TCR lies in tailoring composition and microstructure of the final product.
Commercial ferrite applications usually require a high permeability and/or saturation magnetization. Short magnetic switching times are also highly desirable. Ceramic magnetic materials are currently being used in the fast growing area of high-frequency solid-state devices. The higher resistivity of these ferromagnetic oxides gives them a decisive advantage over magnetic metals. Lowering the high frequency loss is a challenge and many of the properties are sensitive to the effects of heat treatment and composition. For instance, a surplus or deficiency of Fe ions of a few percent can change the resistivity of a magnetic ceramic by several orders of magnitude. Eddy-current losses can be controlled by improving the resistivity of the ferrite. In a more general sense, phase purity, proper oxidation state, large grain size and low porosity all contribute strongly to lowering the loss in ferrites.
The electronics industry relies on printing of patterns of various materials onto substrates to form circuits. The primary methods for printing of these patterns are screen-printing for features larger than 100 μm and thin film approaches for features less than 100 μm. Other subtractive processes are available for feature sizes less than 100 μm. These include photo-patternable pastes, laser trimming, and others.
U.S. Pat. No. 5,801,108 by Huang et al. discloses dielectric pastes formulated from starting materials including a dielectric powder composition, a glass composition such as a borosilicate glass that will melt at about 500° C. to 600° C. and react with the dielectric powder upon firing and partially form a crystallized phase, and a binding material such as an organic binder. The resulting dielectric precursor is a multiphase, dielectric precursor wherein at least one phase is an alkaline earth, transition metal silicate. It is also disclosed that when the dielectric powder to crystallizable glass ratio is approximately 60 to 40 wt. %, then the resulting mixture will densify at approximately 850° C.
Precursor derived printable conductor compositions are described by R. W. Vest (Metallo-organic materials for improved thick film reliability, Nov. 1, 1980, Final Report, Contract #N00163-79-C-0352, National Avionic Center). Vest described only compositions that contained precursors and a solvent.
U.S. Pat. Nos. 6,036,889 and 5,882,722 by Kydd disclose conductor precursor compositions that contain particles, a metal organic decomposition (MOD) precursor and a vehicle and provide pure conductors at low temperatures on organic substrates. However, materials to form dielectrics, resistors, and ferrite materials are not disclosed. Also, formulations for fine mesh screen printing are not disclosed.
U.S. Pat. No. 6,197,366 by Takamatsu discloses methods using inorganometallic compounds to obtain formulations that convert to metals at low temperatures.
Attempts have been made to produce metal-containing compositions at low temperatures by using a composition including a polymer and a precursor to a metal. See, for example, U.S. Pat. No. 6,019,926, by Southward et al. However, the deposits were chosen for optical properties and were either not conductive or poorly conductive.
U.S. Pat. Nos. 5,846,615 and 5,894,038, both by Sharma et al., disclose precursors to Au and Pd that have low reaction temperatures thereby conceptually enabling processing at low temperatures to form metals. The printing of these compositions, however, is not disclosed in detail.
U.S. Pat. No. 5,332,646 by Wright et al. discloses a method of making colloidal palladium and/or platinum metal dispersions by reducing a palladium and/or platinum metal of a metallo-organic palladium and/or platinum metal salt which lacks halide functionality.
There exists a need for low viscosity precursor compositions to electronic materials for use in electronics, displays, and other applications. Further, there is a need for precursor compositions that provide low processing temperatures to allow deposition onto organic substrates while still providing a feature with high conductivity. Furthermore, there exists a need for low viscosity precursor compositions that enable deposition methods that offer enhanced resolution control and the ability to direct-write electronic features onto a substrate.